SOIL PREPARATION

CHAPTER 10

SUMMARY ABOVEGROUND GRAPEVINE RESPONSE • A reduction in available soil vol- ume decreases the grapevine root system and subsequently also shoot growth and yield. One of the first signs of soil compaction is uneven growth which may eventu- ally progress to dead patches in a vineyard. • Under irrigated conditions, soil preparation using a delve plough resulted in higher grape yields than either shallow ploughing or ripping. A similar trial in a differ- ent viticulture region gave similar results, but in contrast to the first experiment, grapevines on delved plots were more vigorous than those on shallow-ploughed plots. • Determination of effective soil depth in the above-mentioned experiments using a penetrome- ter showed a significant positive relationship with grapevine perfor- mance. These studies could, how- ever, not pinpoint optimum soil depth for grapevine performance.

• In a further trial to determine opti- mum soil depth for grapevines, soil volumes were accurately restricted under both dryland and irrigated conditions. Up to the fourth year, results indicated that the optimum soil depths were 80-100 cm for dryland vineyard and 40-80 cm for irrigated ones. Soil depths of 120 cm yielded excessive shoot growth. An important conclusion was that adequate soil depth could compensate for lack of irrigation. This finding will become increas- ingly relevant as the availability of irrigation water decreases due to population growth and climate change. • In conclusion, based on practi- cal observations and field exper- iments, soil preparation in South Africa aims to loosen the soil to a depth of at least 80 cm, but pref- erably to one meter. Normally no further benefit will arise from loosening the soil deeper than one meter.

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